As is well known, the water supply line to cooling and heating equipment such as boilers has various types of deaeration devices (deoxidizing devices) incorporated therein for the purpose of preventing the interior of the device from corrosion. Those deaeration devices are applausively used in recent years as a countermeasure for the generation of red water in the water supply tubes in architectures such as buildings and apartments.
Also, in recent years, washing systems using deaerated water (especially, deoxidized water) have been receiving attention as a result of seeking a washing method without using CFCs (chlorofluorocarbons) in order to prevent the ozone layer from being damaged by CFCs.
A conventional membrane deaerator for the aforementioned use such as shown in FIG. 19 is known. This deaerator comprises a deaerator module (1') and a flow switch (6') provided in a water supply line (3'), a constant flow rate valve (11'), a seal-water use solenoid valve (12') provided in a seal water supply line (9') between the water supply line (3') and a water sealed vacuum pump (7'), and an evacuation-use solenoid valve (13') provided in a vacuum deaeration line (10') between the deaerator module (1') and the water sealed vacuum pump (7'). Therefore, when water (pure water, tap water, well water, and other industrial water) is supplied to the water supply line (3'), the flow switch (6') is activated to drive the water sealed vacuum pump (7') while the two solenoid valves (12'), (13') are opened, whereby a vacuum deaeration process is performed. Then, with the water supply off, the water sealed vacuum pump (7') is stopped, where the two solenoid valves (12'), (13') are closed.
The deaerator with this constitution is capable of processing at normal temperature advantageously. However, its deaeration level is around 0.5 PPM.
Known deaeration systems using deaerator modules include a "deaerator" described in Japanese Patent Laid-Open Publication No. SHO 51-28261 and another "deaerator" described in Japanese Patent Application No. HEI 4-4003. Several other similar inventions have also been proposed.
Otherwise, a deaeration system (not shown) using a deaeration tower is adopted for production of industrial water in the electronics field. This system, however, has difficulty in supplying processed water of a deaeration level (deoxidizing level) below 10 PPB that is required for washing electronic parts such as recent years' LSIs.
As an effective countermeasure for problems in practical use of the aforementioned conventional deaeration system, it could be conceived that the deaeration performance attributable to the vacuum pump is enhanced by improving the deaeration system using a hollow-fiber module as the deaeration means. To achieve this, the following technical problems need to be solved.
With a system using deaerator modules, for example as for the dissolved oxygen concentration of processed water, if the outside atmospheric pressure of the hollow-fiber membrane within the deaerator module is 30 torr (partial pressure of water vapor: 17.5 torr), then an oxygen concentration of about 8 PPM in raw water can be reduced to 0.5 PPM (at 20.degree. C.). However, in order to obtain a dissolved oxygen concentration of 10 PPB or less, the about 8 PPM oxygen in the raw water must be sucked up in a vacuum state of 18 torr (including partial pressure of water vapor). For this purpose, a water sealed vacuum pump having a capacity about ten times larger than that conventionally used is necessitated. Unfortunately, because water sealed vacuum pumps of such large capacities are not manufactured in general, it is actually difficult to reduce the dissolved oxygen concentration to 10 PPB or less.
Therefore, an object of the present invention is to provide an improved membrane deaeration system which is capable of reducing the dissolved oxygen concentration of raw water to 10 PPB or less using a general, relatively small (commercially available) water sealed vacuum pump.
One aspect of the present invention for achieving the above object relates to a construction of the membrane deaerator improved in its deaeration performance by a combination of deaerator modules and vacuum pumps.
Another aspect of the present invention relates to a deaeration system devised so as to enhance its deaeration effect by cooling the seal water for the water sealed vacuum pump or by heating the raw water.
A further aspect of the present invention relates to an embodiment of using a circulation line for circulating the seal water through a vacuum pump as well as to a method of using the same.
A yet further aspect of the present invention relates to a deaerator devised so as to enhance the operating efficiency of the whole system by integrally controlling a plurality of deaeration systems.
The other aspects of the present invention relate to improvements of the individual components according to combinations of hollow-fiber modules and water sealed vacuum pumps and will be described herein in association with the following embodiments of the present invention.